Currently, only high-pressure lamps are used as illumination modules for “optical engines” of data and video projectors, for projection monitors, as well as television sets these lamps emit a continuous spectrum in both visible light and the adjacent ranges (UV, IR). However, only narrow wavelength ranges of the colors red, green and blue are needed to produce an image. For sequential coloration, these colors are utilized individually and sequentially, with the use of a color wheel. The wavelengths not needed in this process are filtered out.
Disadvantages result from the use of high-pressure lamps in connection with the sequential generation of the colors red, green and blue, especially for small, mobile projectors, due to the size and limited serviceable life of the lamp, as well as the required use of a color wheel and UV and IR filters, so that such arrays are very cost-intensive. In addition, light efficiency is low.
To overcome these disadvantages, various light-emitting diodes (LEDs) have been proposed as light sources. When using three modulated LEDs in the colors red, green and blue, the color wheel can be eliminated. Instead, an optical array must be found that, as efficiently as possible, collects, bundles, mixes and homogenizes the light emitted by the LEDs in a large solid angle and displays it on an imager.
Also known in the art are glass prisms for connecting multiple light sources, which are provided with special optical layers (color mixing cubes). Disadvantages include absorption losses and relatively high spatial requirements, as well as high costs.
To connect multiple colored light bundles, arrays of plane mirrors are known which possess dichroitic layers that are adjusted to the colors used, wherein the mixing of two colors into the beam path of the third color normally occurs below 90 degrees, that is, the plane mirrors are positioned at an angle of 45 degrees relative to the optical axis of the beam path of the third color.
In DE 102 37 202.0, a solution is described in which multiple LEDs are arranged directly on the entry surface, on the lateral surfaces or in proximity to the entry surface of a light-mixing rod, such that the bulk of their emitted light is mixed in the integrator and supplied to the light exit surface.
In addition, EP 125148 shows a beam transformation of the light coming from the LEDs by means of fibers, wherein each of the individual fibers is assigned to an emitter. The light from the LEDs is transferred to an integrator through the optical fibers or through fiber arrays. Color management is achieved by switching the individual color LEDs on and off in accordance with the generated color signals. A display computer synchronizes switching the LEDs on and off to correspond to the image data supplied by a computer.
Color combiners for superimposing the individual colors, for example, are proposed for a multi-channel application.
The disadvantages of the known solutions lie, for the most part, in the inefficient use of the light flux emitted by the LEDs during mixing into fibers or a light-mixing rod. Color mixing using dichroitic prism arrays also has its limits in terms of the size and efficiency of the illumination module.
Based on the above, the underlying goal of the invention is to further develop an illumination module, using LEDs as light sources, in such a way that, while minimizing the size of the module, the light efficiency of each of the three base colors of the LEDs, allowing for the technically available light flux, is increased.